Apple co-founder Steve Wozniak says that Apple did not need NeXT, the company that provided the foundation for Mac OS X; he argues that System 7 wasn't nearly as bad as it was made out to be. Wozniak also says that Mac OS 9 was more secure than OS X is now: Mac OS X is built in Unix and is therefore more prone to attacks because people are familiar with the holes in Unix, explained Woznaik. "Some of the holes in Unix are well known. So keeping Firewalls on is more important. And we keep announcing, even our own security fixes, not as many as Microsoft but still we never really had those in the OS 9 days."

That's not what the guys from the Singularity project said: they had the same level of performance for system call with their unoptimised implementation as Linux or Windows.
The reason why they were able to do so is that they are not using the hardware memory protection.